PHYS Biomechanics of Breathing - Week 1 Flashcards
Boyle’s Law
P1V1 = P2V2 (in a closed system, any change in volume will result in a change in pressure).
Chest movement direction, external intercostals…, ribs…, sternum… on inspiration.
Chest moves out & upwards (external intercostals contract, ribs elevate via lateral shaft, sternum flares w sup & ant movement).
Chest movement direction, external intercostals…, ribs…, sternum… on expiration.
Chest moves down & inwards (external intercostals relax, ribs & sternum are depressed).
Pleural effusion
Accumulation of fluid in pleural cavity.
Empyema
Pus in pleural cavity.
Pneumothorax
Air in pleural cavity.
Haemothorax
Blood in the pleural cavity.
Intrapleural pressure +ve or -ve
Always -ve. 756mmHg (-ve as Patm = 760mmHg)
Breathing technique characteristic of pts with low lung compliance
Shallow breathing at a fast rate to ensure inspiration of an adequate volume.
Lungs can expand & inflate due to:
Lung compliance & airway radius
Lung compliance is determined by
Stretchability of the lung tissue & consistency of the lung tissue (collagen fibrils, elastin, fibroblast presence & surface tension of the air-fluid interface lining alveoli).
4 factors affecting airway radius & consequences of each (i.e., bronchodilation/bronchoconstriction).
- Vagal efferent nerves (ACh) -> bronchoconstriction
- Sympathetic nerve supply (NA) -> bronchodilation
- Circulating catecholamines (B receptors) -> bronchodilation
- Inhaled stimuli (e.g., cigarettes, dust, cold air) -> reflex bronchoconstriction.
When does surfactant production begin embryological development.
6-7mths gestation.
Clinical examples of decreased lung compliance
Pulmonary fibrosis, ARDS.
Clinical examples of increased lung compliance
COPD, emphysema.
Character of lungs w low compliance
Stiff, difficult to inflate.
Character of lungs w high compliance
Difficult to deflate, increased elastic recoil.
Spirometry results corresponding to airway radius & lung and chest compliance
- Airway radius - look at the inspiratory and expiratory flow rates and the FEV1/FVC% (see below).
- Lung and chest compliance - look at the vital and total lung capacity, i.e. VC and TLC. We can measure VC with spirometry but not TLC.
Reduced airway radius clinically corresponds to what presentation
Obstructive lung disorders (e.g., asthma, COPD).
Reduced lung & chest compliance clinically corresponds to what presentation
Restrictive lung disorders (e.g., fibrosis).
Normal range for FVC
> 75% - pt should be able to breath out >75% air in first 1 second of max expiration.
Intrapleural vs intrapulmonary vs transmural pressures. State whether each is usually positive or negative.
Intrapleural pressure refers to pressure between parietal & visceral pleura - in pleural cavity. Pressure is -ve due to attempt to move parietal & visceral layers apart which is impossible due to pleural fluid between these two layers (like water between two glass microscope slides).
Intrapulmonary/transpulmonary/intra-alveolar pressure refers to the pressure inside the lungs.
Transmural pressure = intrapulmonary - intrapleural pressures.
+ve/-ve, -ve, always +ve.
What 2 x forces are responsible for preventing alveolar collapse?
Surfactant action & transmural pressure gradient.
Hyperinflation is associated with restrictive or obstructive?
Obstructive as the air can’t get Out -> hyperinflation.
